THE DIGESTIVE ORGANS OF THE ALCYONARIA. 351 
compounds from the inorganic nitrogen salts contained in the 
sea water, but they may also make use of the waste nitro- 
genous animal matter, in which case the alga too would derive 
some benefit from the symbiosis. 
In the reduction in size and function, or complete loss of 
the organs of digestion in corals greatly infested with zoo- 
chlorelle, we have evidence that these algal cells nourish the 
coral to a considerable extent by contributing carbohydrate, 
and possibly also nitrogenous food material in a soluble 
condition. 
Tae Mersogi@aLt Cet Piexos.} 
The cells and fibrils which compose the so called “ meso- 
gloeal nerve plexus” of the Alcyonaria were observed to be 
extremely numerous in some members of the family and com- 
paratively rare in others, while in some instances they 
appeared to be of an unusually large size. 
In his account of the anatomy of the Alcyonaria, Hickson 
(1895, p. 371) calls attention to the fact that, while this 
system of cells and fibrils has not been experimentally shown 
to be nervous in function, yet it is undoubtedly homologous 
with the “ nervenschicht ” described by the Hertwigs in the 
Actinee (1879). Ashworth (1898, p. 209) describes and 
gives admirable figures of a nervous plexus in Xenia which 
he states to be homologous with that of Aleyonium. 
Kassianow, 1903, gives a preliminary account of the 
nervous plexus of “ Alcyonium.” 
In preserved specimens of Sarcophytum, Lobophytum, 
Sclerophytum, and Alcyonium the cells and fibrils vary 
considerably in size, shape, and relative abundance. In 
certain specimens the cells have a stellate form, and are 
provided with numerous long and short fibril-like processes 
(fig. 15, Sclerophytum durum). In some forms they are 
polygonal, with fewer processes (fig. 16, Lobophytum 
1 Preliminary account of nerve plexus. Pratt, 1902, p. 545, and 1903, 
Sect. D. 
